Mixer Circuit Board TroubleShooting

  • Thread starter Thread starter Tremaine
  • Start date Start date
Tremaine

Tremaine

Chancellor of the EOPA
Hello World.
I am a guitar player/song righter, and now a beginner home studio, head bashing, waterly eyed, fool. trying to figure out how to fix my broken gear.
so im looking for some direction. witch way should i go? im mostly intersted in fixing the mixer i just bought off ebay, at this moment, but i cant find anything on the net to help me.
So... help a fellow out wood you?
rock on duders
Tremaine

i posted this under analog mixers and i dont know how to post a link of a post so im gunna copy and paste it. sorry.

Hello World
this is my first post ever, and like many others i dont know excally where it should be.
So i bought a used Behringer mixer off ebay, you can stop laughing now.
it powers up just fine, and is usable, out of the left channel.
I've been searching the net for days now, trying to figure out how to trouble shoot it, but the information is elusive, partially because mixers are driffent and partially because alot of people despise Behringer.
So, when i plug the mic in, the right slider, db meter and output's dont work.
but! if i plug head phones in, they work fine in both channels, but not the slider or db meter. and if i push the solo button in, the decible meter works but not the slider. also if i plug a crapy tape deck into the tape in, the decible meter works fine.
I open it up, discouraged i quickly closed it, then i open it up again. this time i poked around, everything looks connected, everything is sodered to the board. i did not electrocute myself when i pluged it in while it was opened.
now i cant be sure about this, cause things were upside down, but i beleave that for a moment the right channel worked and not the left, i think this happened twice, maybe right after i put the power to it. so maybe a capacitor has failed, and takes amoment to charge to full failure? i dont know. Behringer does not allow us scamatics <sp> not that it would help me much, I own a 9volt multimeter.
So im not sure if this is the site for this, if it aint could someone point me in the right direction please.
I would like to fix this myself, with your help of course, so i can learn, i got some old stereo amps and guitar amps laying around,broken, that i could rob parts off of.
any ideas? how can i test it, i'll take it to a local repair man if i have to but i dont want to.
thanks for you time, world.
peace
Tremaine
 
Well......I'm afraid it's a little more complicated than just jumping in blindly, with little experience and no one there to go over it with you. A+ for spunk, but I'm not sure that you're going to get very far here. A thorough visible inspection is probably the best you're going to be able to pull off.

I'd inspect each capacitor and resistor, etc as best as you can, visually. Looking for signs of burning/bursting, other than that....you'll need to do some research on multi-meter use, that should answer any questions about troubleshooting that you may have.

Behringer schematics are usually in the user manuals. Check their website.
 
35v 1000uf

I've stared at it for hours now, there are burn stains on the case, looks like it took along time to build up, theres also some residue on the side of one of the 35v 1000uF 85'C caps, near the power in. this cap is within 1/8" of the heat sink, and the heat sink gets hot enuff that you shouldnt touch it after the mixer has been on for 20 minutes, while using only one channel, is this normal? the top of the cap in mention is hotter aswell, but this may be due to how close it is to the toasty heatsink .
So i would to test the 35v cap, but i think i read that i cant with a nine volt multimeter cause its only 9 volts, also because the cap is still on the board.
Then i read something about shorting caps, but i think this might be a bad idea, with these perticular caps.
Can i short them with a resister?i got some 47k guitar resistors. i could find something closer, i got some 25v in a broken 10watt amp. Can i use my finger? my body a ground? i think i read something about that too.

iv'e noticed if i plug a crapy tape deck into the tape in's and run the behringer mixer into an older mixers mic inputs, both channels work perfectly, while the mixer is powered off. ?!?! what does this prove? apparently that circuit isnt broken i guess...

im studying up on 'op amps' now, i think im heading in the right direction. its a direction anyway.

Peace World
Tremaine
 
thank you

Thanks for your reply.
but, i would like to make a couple pedals or effect boxes, i found so designs on the world wide web of lies. and i got a bunch of old house amps, and what not lying around. im gunna try to make something out of their guts. i chucked a couple computers together in my day, nothing fancy, but i got them to work, from a pile of random, and freely obtained parts. still working on one. thats the closest thing to a back ground i got in electro tech, i got a 200 in one electronic project lab, and older one, well 3 actually, someone gave me, the labs showed me caps and resistors and diodes, so i got a bit of understanding, but know rules, and no real direction.
so im gunna try to fix my mixer, even if i kills it.
but i heard what you said.
Tremaine
 
Something you should always look for in those cheap boards is either bad connections or loose/fractured solder joints.
That surface mount stuff tends to vibrate that solder point and will actually fracture right around where the lead is sticking out of the solder. Sometimes you can see it if you have a strong magnifying glass and know what to look for. It's sort of a flat gray right around the lead rather than shiny.
Often you can't see it though and really, if you haven't had one pointed out to you it's hard to see. It's a pretty subtle thing.
But if that side of the 'phones is working then you know that side's working earlier in the circuit ..... so that's gonna likely be a bad joint/connection somewhere further down the line.

I think Creamy is probably right. Those can be tricky to track down the problem.
OTOH, that is how people get started fooling around with this stuff so good luck.
 
There are so many components in a Mixer and any one of them failing could cause it to not work properly .... I personally would suggest that you just scrap it and save up for a more reliable piece of equipment , Trying to fix it yourself without major test equipment and a healthy dose of expertize is going to surely be a lesson in futility and frustration ....
Maybe you can sell it to someone for Parts to help recover some of the cost ....


Cheers
 
the battle rages on

thanks for your time people, i appreate it.
Most of what i've read basically said "dont bother, your an idiot for trying, give up before it sends you to the looney bin." im probably half way there now, but it hasent beat me yet.
""..... so that's gonna likely be a bad joint/connection somewhere further down the line.""
Bob said he aint gunna get hooked into this so i guess this is for someone else.
So.... the bad joint must be after all the channels? in the channel bus?
the right slider never works so before that?
To minion: if i could afford a 500 dollar mixer i would gladly take your advice, but as far as i can tell, i cant really get anything better in my price range. i'll probably go for a yamaha MG in the future.
but for now, for 50bucks i got a half decent mono mixer, with gain xlr inputs and phantom power, thats moving up in the world for me. Im a guitar player you know. Im still using my Inkel DM 602 Disco mixer, right now, mostly for singing practice.


Ok so i asked earlyer if i could use my finger to bypass the caps, while the board is running, with minimal risk to life and limb. so im asking again, but this time im not refering to the big caps by the power intake, just the little buggers skattered around the board.

I have searched the net for hours with my modem, and i havent found much guidence, does anyone know of a site that would be more appropate for this? or am i at the right place. I think someone should start a thread telling the basic tale of mixer guts, not me thou, but i guess mixers are all driffent <eccept behringer, who just clone other gear, and then out sourse it. from what i read i dont think the people at behringer can even fix there own gear.> theres lots of amp diy tech out there, wouldnt alot of that be a same?
if someone rote a decent artical on analog mixers, i bet it would get lots of hits *wink wink*
ok, thanks again, people of the world.
Tremaine

btw i just found a mn3207 and mn3102 in a broken realistic karaoke i had kicking around. can anyone say reverb? probably more like fire...
 
If you had a meter and a schematic you'd be nearly halfway there. Having neither of these two is an attempt at futility.

Save your time and use it as a mono mixer and keep your fingers out of energized circuits. Working on an amp and mixer is like working on a car and a motorcycle. They have some of the same parts but they're put together differently.
 
"Bob said he ain't gonna get hooked into this"?
Did you mean me? And if so, when did I say anything like that?

Thing about those cheap mixers is that they are big printed circuit boards with all surface mount stuff and some of it tiny.
If it wasn't powering up someone could likely help you since power supplies are something that can be diagnosed and fixed.
But since the channel is working at one point but not another, you're talking about something in that big surface mount board and I can tell you that even good techs will often choose to send something like that back for repair rather than spend forever trying to track it down.
And even then they don't repair it ...... the factory's repair shop would just replace the entire board and throw the old one away.
So while I'm supportive of working on your own stuff and have said you ought to fool around with it ..... I'll be surprised if you manage to fix it.
I have been surprised before though, so let us know how it goes.
In general I wouldn't worry too much about electrocuting myself in one of those. You might get bit but they don't have the voltages that tube amps do so they're not as dangerous. Just don't grab anything directly hooked to the AC.
 
Go over the pc board with a magnifying glass and look for cracks.

The #1 reason modern crap gear fails that I've seen is because pc mounted jacks that can't flex develop cracks where they are soldered on the pc board. You wouldn't believe how many of those I've fixed. The classic is a headphone jack. I'd always suspect the jacks where they are mounted on the pc board. The cracks can be very small and often require a magnifying glass and a light. I've soldered the breath control jack on my module a zillion times, and the output jacks on my SoundCanvas. I'll bet the majority of Walkmans and portable CD players thrown away are because of this.

Also, depending on what your needs are, you could make a mixer.

I'd been trying to make my own mixer for about 20 years. I just completed the first one that's actually better than anything I could afford, here's some info: https://homerecording.com/bbs/showthread.php?t=295627

I'm selling the 24ch of Yamahas (DMP11's) now, I paid $4,500 for them but my homemade mixer is far better.

Man I wish I knew this 20 years ago! I went through a Soundcraft, a Tascam and 3 Yamaha's and I could have made my own mixer all along and saved a lot of money.

There are some improvements to the circuit since that last schematic. I'm using a pair of Summit compressors (expensive) as make up gain and that makes it sound warm and analog.

I've never tried an Art VLA tube compressor, but there's a chance it could be used as the gain stage of a mixer like mine. I've never liked Art stuff but the reports on that unit are encouraging. Even a decent home stereo preamp could be used.
 
dintymoore said:
Go over the pc board with a magnifying glass and look for cracks.
The #1 reason modern crap gear fails that I've seen is because pc mounted jacks that can't flex develop cracks where they are soldered on the pc board. You wouldn't believe how many of those I've fixed. The classic is a headphone jack. I'd always suspect the jacks where they are mounted on the pc board. The cracks can be very small and often require a magnifying glass and a light. I've soldered the breath control jack on my module a zillion times, and the output jacks on my SoundCanvas. I'll bet the majority of Walkmans and portable CD players thrown away are because of this.
Click to expand...
yep .......
Lt. Bob said:
Something you should always look for in those cheap boards is either bad connections or loose/fractured solder joints.
That surface mount stuff tends to vibrate that solder point and will actually fracture right around where the lead is sticking out of the solder. Sometimes you can see it if you have a strong magnifying glass and know what to look for. It's sort of a flat gray right around the lead rather than shiny.
Often you can't see it though and really, if you haven't had one pointed out to you it's hard to see. It's a pretty subtle thing.
Click to expand...
yep .......
 
Yep, that's right. :)

It hardly ever happened in gear like old Fender amps where the jack was panel mounted with wires that could flex attached to it.

Any time you have something like an input or output jack that will only work when you pull it to one side or lay something on it it's probably that problem.
 
something else similar that I see is those big stupid computer ribbon cables that are soldered right to the board. They'll vibrate and do the same thing.
I have a Hot Rod deVille that had 4 of them connecting the pre to the power section. I'd have to resolder them about once a year and it was a PIA.
Finally I just yanked them out and replaced them with 32 individual wires.
 
aux 2 pre/post soilderless?!?!!

I must say im glad to see some input, its much apre see a ted <even if i cant spell it.>

"Bob said he ain't gonna get hooked into this"?
=
your quote "Thats it for me in this thread. I'll only eat the bait once .... voxxy"
i didnt realise it was a quote, made me think you were running far away from my thread.

Dintymoore: The info on the jacks makes alot a sense, since their the only thing getting moved/jerked around. thanks for that. Im very happy/inspired to hear, that you <a human like me, i assume> have made a worthy mixer. im gunna try, i figure it might take a couple years to finish, but maybe not, i got some time right now, so im gunna try to learn how. im loading your link now... i want an analog mixer, i think digital feels souless, I dont think its right that much music today is recorded without ever making a noise. i mean theres noise during playback, and threw monitor speakers but not in the air. in phyisical reality. just my opinion. <I,I,I,I,I, reread that>

so i found what i beleave is a discrepency.
On the mixer circuit board, on the 4 mono channels, there is a spot where you can set the AUX2 from post to pre
manual says: " Mono channel aux sends 2 are post-fader. if you want to convert them... cut the "post" track , add in "pre" link. k, so
on the first channel these 3 holes thou, unaltered, have no soider in the holes, while the other 3 sets do <chan 2,3,4>. could this be my problem???
i hope so

Thanks for your time people of the World, Peace.
Tremaine
 
A voltage regulator should not get that hot in a good design, and if the cap's vents are swelled or popped, that is likely your problem right there. If the "residue" is just glue around the base of the cap, that is normal.

You say you have a 9V meter, but if you mean it uses a 9V battery, that doesn't mean it can't test higher voltages. If it is truly limited to a 9V range, then you'll need a better multimeter. See my thread on that topic, any $10 multimeter should have a VDC range up to 200V, at least.

You can't really harm yourself inside this mixer EXCEPT for the primaries of the power transformer. Those are at 120V (240V in Europe). So figure out where those are, and DON'T TOUCH THEM. Once the power comes off the transformer secondary, it is low voltage and generally safe (although if you are sloppy with your meter probes you can cause groovy sparks and fry components).

Now, if you find a problem in the power supply and fix it, it could have been caused by a failure elsewhere, so your new parts might fail again until you find the problem downstream.

Good luck . . .
 
per/post fader jumper?!

hey MsH, thanks for clearing up the 9volt thing, i dont know where i got that idea, but i retty much gave up on using my DMM, until you said that.
So anyone have anyideas about the alt post/pre thats un-soldered, its the first channel, so it could effect all my stereo after that point right?
can i test it without solder, i dont dare try my first attempt at circuit board soldering on this board, i'd reck it for sure. can i jam a wire in the two holes? theres already a track connecting them i can see, just no solder... can i use my finger? im gunna try...
Thanks World, Peace
Tremaine
 
Short Fader

So i was poking around inside the mixer somemore, with my fingers and a knife, witch i found more percise then a screw driver, and i learned a couple things. first off my finger dont make sparks! probably cause im grounded?
I noticed the mic modules <sp> get quite warm, when theres nothing pluged into them, i wouldnt call them hot thou, and i wood imagine this is normal?
I think the right fader has got a bad ground or something because... where the fader connects at the very bottom of the board, there are four pins, and if i touch the first one with my finger it shorts out and the board trips off for a couple seconds, the fader wont trip if i touch the other three and if i touch them on the left side nothing happens <left side works fine> but will trip if i touch the left sides 8 tiny resisters<i beleave> or at least buzz, and touching the 8 on the right side does nothing...
So, from my guitar training <self tought> i learned that a pot turned up to ten is effectively doing nothing and it bleeds off treble to ground as you turn it down, im gunna try to cause a direct short from one side of the slider to the other, taking it out the equation. So here goes round 12... well day 8 or 9 anyway...
any advice?
Peace World.
Tremaine
 
Last edited:
fad-0172

I found the part number, 60mm mono 50k alps, fad-0172 <fad-0173=stereo>
but i cant find a layout for it, no pdf like IC's have.
I figure they arnt all wired the same so perhaps i can get a little insight from someone?
i guess the part is made for behringer gear only.
im assuming its mono, cause theres a left and a right for the main mix, and i figure the only stereo faders are on the stereo channels and the alt 3/4 chan.
how should i bypass it for testing, im thinking a peace of wire or two, do i need two? or three? it would be three if it was a guitar pot i beleave. power, neutral and ground.
Peace World.
Tremaine
 
btw: the residue around the big caps is not glue, its a light smoke stain, but i think it probably built up over a long time.
 
Victory is ours! the conclusion.

So i found some info on alps faders, found the parts number and all, and also found out its a stereo fader, thou its mostly used in mono on my mixer, only one side is hooked up. Im going to order one, adventually. $10, im gunna try and find a better one that will work first, something that feels better, and fits.
I desoldered the last stereo channel and moved the fader to the right main channel, to do this i used a solder kit, with 30w iron, solder sucker<really sucks.> a crapy stand and flux center no lead solder. i got from 'the source' <witch was crapy shack> for 20$$ canadian, i dont think i could do better on ebay, not after shipping. The solder sucker didnt suck the way i had hoped for, i think maybe i'll use desolder braid next time.
Any way, i tryed it, and it worked! thank you, thank you, thank you. without you people <or robots> this would probably be a mono mixer for life, or parts.

the moral " Try try again, and dont be vexed by discouragment. "

Thank you World, Peace
Tremaine
 
You must log in or register to reply here.
Back
Top